Unless otherwise indicated herein, the materials described in this section are not prior art to the claims and are not admitted to be prior art by inclusion in this section.
In a typical cellular wireless communication system, the air interface between a base station and served mobile terminals may define a downlink (or “forward link”) for carrying communications from the base station to the mobile terminals and an uplink (or “reverse link”) for carrying communications from the mobile terminals to the base station. In various implementations, these links may be defined on or more carrier frequencies or blocks of frequencies. Furthermore, on each link, various channels may be defined through techniques such as time division multiplexing, code division multiplexing, and/or frequency division multiplexing.
In one implementation, the downlink may be divided over time into a continuum of timeslots (i.e., “transmission time intervals” (TTIs)), and the base station or associated equipment may be arranged to transmit data, such as bearer traffic (e.g., user data) and control signaling (e.g., paging and other overhead messages), to mobile terminals in those timeslots. In such an implementation, the base station or associated equipment may dynamically schedule transmission of data in particular timeslots and may then transmit the data according to that schedule.
To help overcome errors that may arise in wireless data transmission, the base station and served mobile terminals may also be arranged to apply a hybrid automatic repeat request (hybrid-ARQ or HARQ) process. In such a process, when the base station is going to transmit a data packet to a mobile terminal, the base station may repeatedly attempt transmission of the packet to the mobile terminal in sequential (e.g., interlaced) timeslots, until the mobile terminal confirms that it successfully received the packet or until the base station completes a maximum number of attempts without receiving such confirmation.
In practice, for instance, the base station may add more error correction with each subsequent attempt and/or may transmit various portions of the packet with various error correction coding in each subsequent attempt, in an effort to have the mobile terminal ultimately receive enough data to constitute or facilitate uncovering the packet as a whole. For example, if the packet payload comprises the elements ABCD, the base station may transmit in a first timeslot the full payload ABCD plus some error correction coding. If that transmission is insufficient to allow the mobile terminal to uncover the payload (e.g., due to errors in the transmission process), the base station may then transmit in a next timeslot a portion of the payload, such as ABC, plus some additional error correction coding. And if that transmission is still insufficient, the base station may then transmit in a next timeslot another portion of the payload, such as BDC, plus more substantial error correction coding. This process may continue until the packet transmission is deemed successful or until a predefined threshold number of timeslots is exhausted (in which case the transmission would have failed).
During this packet transmission process, the mobile terminal may transmit a hybrid-ARQ message to the base station in response to each transmission attempt from the base station. In particular, for each transmission attempt that does not result in the mobile terminal having successfully received or uncovered the complete packet payload, the mobile terminal may transmit to the base station on the uplink a negative acknowledgement (NAK), to prompt the base station to engage in a next transmission attempt. On the other hand, if and when the mobile terminal received and uncovered the complete packet (e.g., the packet transmission and any associated decoding by the mobile terminal was successful), the mobile terminal may then transmit to the base station a positive acknowledgement (ACK), to inform the base station that transmission of the packet was successful, thereby completing transmission of that packet.